Interferon-gamma production in antigen specific T cell response: quantitation of specific mRNA and secreted protein.

Interferon gamma (IFN-gamma) production as a measure of cellular sensitization was studied by detection of the cytokine in culture supernatant by enzyme immunoassay (EIA) and by measuring cellular mRNA using the reverse transcriptase polymerase chain reaction (RT-PCR) method. These assays were compared to the standard lymphocyte proliferation assay as a marker of T cell responsiveness to foreign antigens. When blood donors seropositive for herpes simplex virus (HSV) were compared to seronegative donors, all measurements of cellular sensitization separated the groups without overlap. There were significant correlations between the IFN-gamma mRNA titre and the secreted IFN-gamma (r = 0.57, P = 0.03), and the proliferative response and the secreted IFN-gamma (r = 0.78, P = 0.001), as well as between the IFN-gamma mRNA titre and the proliferative response (r = 0.78, P < 0.001). When tetanus toxoid (TT) responses were studied in immunized subjects, a wide range of responsiveness could be seen and correlation between various measurements was poor. However, constant individual levels of the cytokine production were demonstrated. Six people who had received their last TT booster vaccination more than 5 years ago were revaccinated and repeatedly studied. An increase in the levels of produced IFN-gamma could be seen in all subjects and two who lacked a lymphocyte proliferation response developed it after revaccination.